The most interesting part of a Lunar eclipse is during totality when the darkened Moon picks up a faint red glow (the "Blood Moon"). Numerous stars are usually visible at that time, being normally invisible when the Moon is full and bright.
Geotripper
News and views from the geologic realm
Friday, March 14, 2025
The First Lunar Eclipse of 2025
The most interesting part of a Lunar eclipse is during totality when the darkened Moon picks up a faint red glow (the "Blood Moon"). Numerous stars are usually visible at that time, being normally invisible when the Moon is full and bright.
Thursday, February 20, 2025
An "Extinct" Fish Finds Life Again in a Parched Desert: The Saga of the Shoshone Pupfish
The pupfish habitat at the springs in Shoshone, east of Death Valley National Park |
How they survive is not difficult to understand: despite the aridity of the California desert, there are sources of water. There are permanent springs and pools of water scattered all around Death Valley and the Amargosa River Basin, and the fish have adapted to life in waters that might be hot, cold, fresh, or salty.
How they got there in the first place is a little trickier to understand. Our climate has been subject to huge variations over the last two million years, and more than a dozen times, it got much cooler and glaciers developed and expanded, especially in the Sierra Nevada mountains. Some of the meltwater from those glaciers flowed into the deserts of the Basin and Range province and accumulated in huge freshwater lakes. As a lake basin filled (such as at Mono or Owens Lake), it spilled over into the next lake basin until a network of lakes extended from the Sierra Nevada to Death Valley. The Amargosa River flowed through western Nevada, also ending in Death Valley. So there was plenty of water once upon a time.
At some point in time, a connection was made with the Colorado River, and fish were able to make their way into the network of freshwater lakes, and they thrived. But as each glacial stage ended, the lakes would begin drying up and most of the fish lost their habitat and went extinct. But those very few species that could adapt quickly enough took refuge in the rare and isolated springs and pools. A few, including the Lahontan Cutthroat Trout survived in the cold streams, lakes and rivers of the eastern Sierra Nevada. Those trapped in saline waters had to adapt to the salty conditions. Some fish adapted to high temperatures, and unlike pretty much any other fish in the world can survive in water that reaches a hundred degrees or more.
One of my very few photos of the Devils Hole Pupfish, taken from around 100 feet away. |
Perhaps the most famous of these fish is the Devils Hole Pupfish (above), found in a single cavern opening in the Ash Meadows National Wildlife Refuge (the spring officially lies in an outlier of Death Valley National Park). Their story is compelling, but they are not the fish I'm discussing today. You can read about them if you wish here or here.The various populations of pupfish survived for thousands of years in isolation from human developments. But the colonization and occupation of the desert by miners and ranchers spelled doom for some of them. One species, the Tecopa Pupfish, was driven extinct pretty much in an afternoon when pipes were installed at the one spring where they lived. A similar fate apparently happened to a different subspecies, the Shoshone Pupfish (Cyprinodon nevadensis shoshone) in the 1960s as springs in that area were developed for domestic use at the village of Shoshone. The species was declared extinct in 1969, as none could be found anywhere.
Improbably, a small population of the fish actually survived the devastation of their original habitat by taking refuge in a nearby irrigation ditch, unnoticed by anyone. In 1986 they were rediscovered, and a cooperative effort by the private landowner and several environmental organizations resulted in a resurrected habitat. This habitat was actually expanded to three pools and some artificial off-site refuges as well. Despite visiting Shoshone yearly for the last three decades, I never heard about the efforts being made on behalf of the fish's well-being.
That changed last week when I found out that a nature trail had been constructed, and interpretive signs posted that allowed for some close viewing of the diminutive fish (as well as another highly endangered creature, the Amargosa Vole). The site also serves as an excellent habitat for a large variety of birds, and we saw Western Bluebirds, Yellow-rumped Warblers, White-crowned Sparrows, a Costa's Hummingbird (a life-lister for me) and we could hear Verdins chattering away in the brush.
The trail is just off the main highway in Shoshone, and the locals seem proud of the efforts and can easily point the way to the trailhead, next to the local school. If you ever travel to Death Valley from the east, you can't miss the town. It's the only gas station and food stop for many miles. Don't forget to stop in at the local museum for a look at the Columbia Mammoth fossils on display inside!
Monday, December 30, 2024
Strange Doings in the Sky Today. What the Heck is a Circumzenithal Arc?
I made use of a highly technological sun-blocking tool that I have in my pockets sometimes to try and bring out the colors a little better. In my capacity as an earth science instructor I generally teach about climate and weather, but phenomena related to the refraction of light off hexagonal ice crystals in the upper atmosphere gets lost in the concerns over global climate change and that sort of thing. So I haven't kept up the finer details of atmospheric refraction effects, and had to get a refresher about what I was seeing.
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Source: Meteorology Today by Don Ahrens |
There were five phenomena happening at once here, all related to the refraction of light in ice crystals in the upper atmosphere: a 22 degree halo, part of a 46 degree halo, two sun dogs, an upper tangent arc, and high above, the circumzenithal arc (the upside-down "rainbow"). I read that the arcs are not uncommon, but are noticed less because they tend to occur overhead where people don't tend to look. I didn't see it myself until I stopped on the way home to try and catch the arc again. It can be seen in the picture below.
Beautiful things can find you any time. You just need to watch for them!Saturday, December 28, 2024
About That Bucket List...What Would You Do To See These Places?
Horseshoe Bend on the Colorado River |
Grand Canyon National Park |
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Angels Landing Trail in Zion National Park, Utah |
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Mesa Arch in Canyonlands National Park |
Petroglyphs on the plateau |
Petrified Forest National Park |
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Canyonlands National Park, Utah |
The cost of the trip (still to be officially determined) will be about $1,100 plus the cost of tuition (Currently $46 per unit for California residents, and around $225 per unit for out-of-state residents). The cost includes transportation, food, camp fees, and entrance fees. Participants would want to bring a few dollars along for showers, laundry, and souvenirs. The food is tasty and plentiful (everyone helps cook and clean!), and the school vans...are vans.
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House-on-Fire Ruin, Bear's Ears National Monument |
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Bryce Canyon National Park |
Wednesday, December 25, 2024
The Simultaneous Seasons of California (and a peek at Half Dome)
It was a beautiful Christmas day here in the Central Valley, one of the prettiest I can recall. The storm that blew through yesterday was gone, and the winds were enough to prevent the fog from setting in. I took a walk along the Tuolumne River Parkway Trail in Waterford, and was gifted one of those rarest of things: a clear view of the beautiful Sierra Nevada. And of course it was the moment of three simultaneous seasons of California.
Yes, it's that time of year in California when three seasons occur at once. Sure, the calendar says it's winter and all, and that is certainly true in the high country of the Sierra, buried under feet of snow. But here in the valley, the last leaves are finally falling from the Valley Oak trees along the river, but with the rain has come the promise of spring as the grass sprouts and spreads a layer of green along the bluffs above the Tuolumne River.The gift of enjoying the panorama of the Sierra Nevada Crest is rare in our valley. Although my little town sits at the very edge of the Sierra Nevada foothills, the mountain range is a tilted block of crust that slopes gently westward. As a consequence, the high peaks of the Sierra Nevada lie 40-50 miles away. The view of the peaks is generally obscured most of the time, for reasons both natural and artificial. In winter, an inversion layer develops that keeps a barrier of fog and mist that prevents any viewing of the mountains. In the summer and fall, dust and smog obscure the view. It is most often at the end of storms that the mountains are revealed in their full glory like they were today.
The Tuolumne River is one of the two main rivers that drain Yosemite National Park (the Merced River is the other. So the view from my trail encompasses much of the roughly 1,000 square miles of the park (for perspective, Yosemite Valley itself is only about 7 square miles). The view above includes most of the high peaks of the park, including the highest (Mt. Lyell). The diagram below, courtesy of CalTopo, provides the names of the peaks seen in the photo above.
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Analysis courtesy of CalTopo |
Still not obvious? I've outlined the top of Half Dome below, with the ridge of El Capitan below and slightly right. There is a much better view to be had of Half Dome from about 5 miles south of the trail near the junction of Keyes Road and S. Hickman Road. It's been a bit of fun arguing over the years with people who are absolutely sure that Half Dome can't be seen from the valley for all kinds of logical reasons (the photos of course are photoshopped or whatever, which by the way is not a skill that I have).In any case, the view was one of the best gifts of this beautiful day. I hope your Christmas and other celebrations were wonderful, and that you have a great new year! Thanks for reading!
Monday, November 11, 2024
In the Heart of the Devil: The Damning of Del Puerto Canyon
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This beautiful canyon is under serious threat |
We just explored the heart of the devil: the so-called Diablo Range. It is one of the largest individual ranges in the province, running for around 150 miles from Mt. Diablo and the Carquinez Strait on the north to the Coalinga area in the south. The region is largely undeveloped, and few paved roads cross range. We followed one of those few roads, the one that traverses Del Puerto Canyon. It's a one-of-a-kind experience, the equivalent of driving into and through the crust of the Earth and into the mantle below. It is the path to the nether-world that has often been called the home of the devil.
Del Puerto Canyon lies just west of the Central Valley town of Patterson. A paved road, state route 130, connects Patterson with the Santa Clara Valley, but anyone thinking it would make a shortcut between the two localities is in for a rude awakening: curvy, narrow, with steep drop-offs, it is not a road for the faint-of-heart. It also has some extraordinary scenery and some absolutely fascinating geology.
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One of our students discovered an ammonite fossil on this trip! |
The canyon also has a place in the history of California paleontology. The 25,000 feet of oceanic sediments provide an extensive record of fossil species, including the clams, snails, ammonites and shark teeth that are expected in such environments. Mesozoic marine reptiles have also been found in the region, including plesiosaurs, ichthyosaurs, and a new species of mosasaur, Plotosaurus bennisoni. The canyon was also the site of the discovery of California's first dinosaur, a species of duckbilled dinosaur called Saurolophus. It was discovered by 16-year-old Al Bennison of Gustine in 1936. We found a single fossil this trip, an ammonite. Someday, it'll be a dinosaur, right?
To me, the most interesting rocks are found in the upper canyon. The mantle of the Earth is a 1,800-mile-thick layer that starts at a depth of 15 or 20 miles beneath the continental crust. It is generally composed of a rock called peridotite or dunite, made up of the mineral olivine with varying amounts of pyroxene and various ores of chrome, mercury, magnesium, and copper. Peridotite is chemically unstable in surface conditions and alters mostly to serpentine. Many of the rocks we observed showed some degree of alteration. The rock below that looks like alligator skin (below) is composed of fractured chunks of pyroxene (the reddish-brown) and serpentine (the green fracture filling).
In a few spots one can find some relatively unaltered peridotite (below).

We also found some samples of chromite ore. Chrome contributes to the production of stainless steel and has applications in forming armor. During peacetime, there are cheaper sources of chrome overseas, but during wars the supplies may be cut off. During the world wars, chromite was mined in the upper canyon and transported by rail down the canyon to Patterson to be processed.
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The little black grains are chromite |
Del Puerto, ("the Gate") Credit: Elias Funez, Save Del Puerto Canyon |
Thursday, October 17, 2024
What We All Think We Know: Myths and Misconceptions about California and Earthquakes for the Day of the Great Shake-Out!
It starts with a modest little quiz....
True or False?
- California is going to fall into the Pacific Ocean
- The San Andreas fault causes all California earthquakes
- California has more earthquakes and bigger earthquakes than anywhere else
- The ground opens up and swallows people during earthquakes
- Psychics and animals predict earthquakes
- We in California are waiting for the "BIG ONE"
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Comic art courtesy of Zeo |
California is going to fall into the sea: true or false?
This is one of those persistent statements about California earthquakes that everyone "knows", even if they live in New Jersey. Many people would say: false.
Here's the correct answer:
True!
In fact, not only is it going to happen, it already has.
Check out the NASA photo above. When we speak of California, we often forget that most people are only thinking of one part of California: Alta California (upper California). The image above reminds us that Baja ("Lower") California is also part of our geography. And Baja has already "fallen" into the Pacific Ocean, in a reasonable interpretation of the statement. Baja was once connected to the Mexican mainland, and has been a peninsula for only the last four million years or so. It is the beginning of a massive rift that will ultimately tear Alta California apart, and send it traveling northwest at all of two inches a year. The two inches per year will actually be taken up by large earthquakes shifting the landscape 10-15 feet every century or so.
In 20 million years, the Dodgers and Giants will again be crosstown rivals (yes, I stole this joke from the DVD "Planet Earth"). In 70 million years, California may slam into the south margin of Alaska, pushing up another high mountain range.
Want to see how this happened? Tanya Atwater of UCSB, the plate tectonics pioneer who figured out the origin of the San Andreas fault, has a series of excellent animations available for download at this site. If you have a fast connection, try this one (50 mb).
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Courtesy of Tanya Atwater. See the animation here. |
So indeed, it could be a good idea to buy up some property in the western Mojave Desert to be ready for your oceanfront views...in ten million years...if you want to wait that long.
What? You thought the question was about California falling into the sea during one earthquake? Really? Like the movie 2012? Not gonna happen. That's tabloid stuff. Aliens kidnapped me last week too.
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Art by Zeo |
Question #2 on our short quiz is:
All California earthquakes happen on the San Andreas fault - True or False?
A crowd at a recent lecture I gave, California residents all, were up to date on this one. Not a single audience member said "true", and they were right. On the other hand, lots of people don't live in California, and they might not be quite as knowledgeable about all of California's faults (double entendre intended). So a few illustrations may be helpful. First of all, where do the earthquakes in California happen? See the map below...
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Map courtesy of NDEDC, UC Berkeley. Follow the link for an interactive version. |
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Map courtesy of NCNDE, UC Berkeley. Follow the link for an interactive map. |
Question three: California has the biggest and the mostest earthquakes in the world. True or False?
I know that "mostest" is not really a word, but it somehow seems to fit well in the question of the day (a little like Stephen Colbert's 'truthiness'). So, what is the answer? My California audience is usually a little divided on this one, but mostly fall into the "false" camp.
So let's check on some data. If you look at the maps above, you can see that California certainly has a great many earthquakes, perhaps 10,000-15,000 year, and some of them are rather considerable.
There have been three earthquakes in the last 150 years that are thought to have approached magnitude 8 in size: 1857 at Fort Tejon, 1872 at Lone Pine, and 1906 in San Francisco.
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San Francisco earthquake of 1906 |
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Fault scarp from 1992 Landers earthquake. Photo by Garry Hayes |
Those are a lot of earthquakes. So let's take the "biggest" issue first. The quake in Japan that destroyed the nuclear power plant and produced the Pacific-wide tsunami was magnitude 9.0. The quake in Sumatra in 2004 that produced the horrific tsunami in the Indian Ocean was magnitude 9.1. So, California doesn't have the biggest earthquakes. Not even close (but check for the wild card issue below, however).
There is a great deal of confusion about the nature of the magnitude scale for measuring earthquakes. It is not a 1-10 scale, for instance, even though literally all recorded earthquakes fall within that range. It is open-ended, and quakes of greater than magnitude 10 are technically possible, but not likely from terrestrial origin. It would take the impact of an asteroid miles across to cause a quake larger than about 9.5 on the magnitude scale.
The biggest confusion concerns the relative size of quakes. Magnitude is a measure of the energy released when an earthquake strikes. A magnitude 9 quake is not just a little bit bigger than a magnitude 8. It is exponentially larger, by a factor of 32. To put it a different way, a magnitude 9 quake releases an amount of energy that is equivalent to 32 magnitude 8 earthquakes!
It gets worse: Since a 9 is 32 times more than an 8, and an 8 is 32 times bigger than a 7, a magnitude 9 quake is more than 1000 times larger than a 7 (32x32).
A magnitude 9 quake is the energy equivalent of more than 1,000 magnitude 7 earthquakes...
Put another way: the Japan 9.0 quake released more energy than all of California's historical earthquakes combined.
The story is pretty much the same with the total number of earthquakes. California has a great many smaller quakes, but just about any subduction zone around the world has more. Even in the United States, Alaska has more earthquakes than California (as well as the second-largest earthquake ever recorded in the world, the 9.3 magnitude Good Friday quake of 1964).
So why does California get this reputation of having an inordinate number of earthquakes? I feel compelled to blame the way news is reported in this country. Cable and local news coverage of earthquakes is atrocious for the most part, with badly misinformed reporters and news-readers (I don't consider them to be news anchors or journalists anymore). There is a tendency to display blood and gore over actual conditions on the ground. The media will spend weeks talking about an earthquake in Los Angeles or San Francisco that kills a few people and practically ignore monumental tragedies in Pakistan or Iran where tens of thousands of people have died.
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An offset curb on the Calaveras fault in Hollister, CA. It isn't the San Andreas... |
True, but only in Hollywood....
Indeed, it is a staple that if an earthquake happens in a movie, somebody is going to be hanging by their fingernails on the edge of a vast deep chasm that has opened up beneath their feet. In the third Indiana Jones movie, for instance, and in last year's 2012, again, and again, and again. And again.
For the reality-based world, the possibility of being swallowed up in the earth during an earthquake is far more unlikely. The problem is that earthquakes are generated by the stress built up along fault lines where vast blocks of rocky crust are in contact. The shaking begins when the rocks rupture and begin slipping. They don't separate. In some faults (thrusts) the stress is compressional and in others (strike-slip) the stress is lateral. Not much chance of openings occurring in either situation. The third type of fault, termed normal faulting, the stress is extensional, which could conceivably result in the stretching of the crust and formation of fissures, but more often, one side slips downward, as can be seen in the picture below, from the 1954 Fairview Peak earthquake in Nevada.
It is true that small fissures will open along fault ruptures in some situations. I saw many of these when I visited the Landers area a week after the 7.3 magnitude earthquake in 1992. The fissures were only a few inches across and no more than a foot or so in depth. Geologist Mary Hill does mention one instance where someone was killed in a fissure that opened up in a 1948 quake in Japan, but that hardly represents a pattern.
One other effect of large earthquakes is the production of slope failures and landslides, during which large fissures might open up. The Turnagain Heights liquefaction event during the Alaska earthquake of 1964 is a stunning example. Weak saturated sediments underneath the housing project were severely shaken, causing the whole landscape to break up and flow towards the adjacent bay, destroying the dwellings at the surface (I've included two pictures derived from my old slide collection, but I'm afraid I don't know who to attribute them to; I will add credit if someone can clue me in. They may be from a USGS collection).
In the 1906 San Francisco earthquake, there were not any claims of swallowed people that I know of, but there is the famous tail/tale of Shafter's cow, which was swallowed up by the San Andreas fault. In the aftermath, only the poor bovine's tail could be seen at the surface. The story apparently became widespread, but in a letter from 1966, some locals recalled that the poor cow had actually died the night before. The earthquake produced a convenient fissure, the farmer tossed in the carcass, and when reporters showed up asking questions about the poor animal, farmer Shafter decided not to kill a "good story".
Question 5: Psychics predict earthquakes: true or false?
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Comic art by Zeo (with slight modifications by Geotripper) |
My audiences and readers are skeptics and non-believers, to be frank, and usually come down firmly in favor of "false" for an answer. So they are a little surprised when I tell them the actual answer:
TRUE!
Think about it a moment, and you will realize that the statement is in fact true. Psychics predict earthquakes all the time. All the time, and then some more. Earthquakes are one of their most common predictions, more popular I think than predictions about aliens.
That leads to a revised question: Do psychic predictions about earthquakes come true?
My readers are usually onto me by now, and they will say that psychic predictions are invariably wrong. I set them straight. I say "Psychics predict earthquakes all the time, and are almost invariably correct".
I support my contention with a collection of predictions that I googled in about five minutes. I refuse to link to each of them because I have no interest in promoting their websites. If you want to find them, google the statement and it shouldn't take long to dig them up.
- Both earthquake and out of control fires will effect California causing devastation and loss [of] life.
- There will be a violent earthquake, one of the strongest on record.[no location noted]
- My California earthquake prediction: yes, there WILL be an earthquake in California. I am not saying it will be along the San Andreas Fault or that it will be major. …I am also not saying when.
- I keep seeing the year 2011 like a pulsating animation within visions of major earth shifts in my home state of California. Dates perceived in months or years could be argued to have limited value in forecasting a time because we psychics move our consciousness in large spans of time and cover broad areas of locations and events.
Wild Weather Predictions
- Category five hurricane wipes out Miami.
- The worst mudslides in California’s history will occur.
- Mount St. Helens erupting.
- Earthquake Seattle, Washington.
- Earthquake Chicago, Illinois.
- Part of the polar ice cap melts.
- Wildfires spread to Beverley Hills and Los Angeles, Brentwood.
- More tsunamis Sumatra Indonesia, Alaska, Hawaii and Japan.
- A great earthquake in Los Angeles, San Francisco and San Diego.
- Earthquake Lake Tahoe.
- Earthquake Toronto and Quebec.
- Earthquake Oregon.
- Earthquake Grand Canyon.
- Earthquake New York, Alaska, Japan, Greece.
- Earthquake British Columbia, China and Iran.
- Tornado in California.
- Floods Amsterdam, Holland, Rhine River, Germany, Bangladesh, Great Britain. Venice, Italy, Gulf Coast of Florida and France.
- Tsunami Malibu, California.
- Wildfires Greece, Australia, Texas, Hawaii.
- Mudslides in India, California.
- Typhoon in Taiwan.
- Tornadoes Oklahoma, Indiana, Texas, Illinois, Tennessee.
- Great earthquake Rome and Naples, Italy.
- Huge snowstorm and blizzards up the eastern seaboard affecting the great lakes – Toronto, Chicago, New York, Boston, etc.
- Earthquake Yosemite and Yellowstone Park.
Soooo...psychics accurately predict earthquakes. Well, guess what? I can predict earthquakes too! And I can be more specific than the average psychic. Here goes..
I predict that within the next week:
- 200 earthquakes will occur in California,
- Of these, there will be a magnitude 4 quake in southern California, most likely in the Colorado Desert near Salton Sea.
- There will be a magnitude 3 earthquake in northern California, most likely north of the Bay Area, somewhere around Clear Lake.
- There will be a larger quake at the Vanuatu Islands in the Pacific Ocean, quite possibly in the magnitude 6 range.
- There will be a magnitude 5 earthquake offshore of Japan.
You can do that, but please note that my predictions have something in common with psychic predictions: the predictions are totally and absolutely useless to anybody. They are about as useful as predicting that the sun will rise in the east tomorrow. Why? Because like the sun rising, earthquakes happen all the time, and they tend to happen in the same general places, mainly along tectonic plate boundaries (along with a few near hot spots like Hawaii or Yellowstone). It sounds impressive that 200 earthquakes will happen over the next week in California, but that happens nearly every week.
Earthquake prediction is a serious business. On the one hand, a timely prediction can save lives. But a prediction made by a credible source that doesn't come to pass is a real problem. Like the boy who called "wolf" once too often, later predictions would be ignored. Charlatans who make spurious predictions can cause panic and unnecessary stress in an uninformed population (such a prediction in 1990 caused the population of St. Louis and surrounding region to close down businesses and leave town, and also caused a media circus).
An earthquake prediction, in order to save lives, must have three elements:
- the time (within a few days at most)
- the location (specific)
- the magnitude and depth
Psychics: give up the earthquakes. Stick to the lives of the Hollywood stars. They're more predictable anyway.
Question 5 B: Animals predict earthquakes...true or false?
My answer to this one?
??? Who knows???
The problem is perceived cause and effect. Many people who experience strong earthquakes recall strange behaviour by their animals, and link that behaviour to the quake. The problem is that animals may behave strangely in many circumstances that are not followed by a strong earthquake, but the behaviour is not noticed or remarked.
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This animal is clearly predicting an earthquake. Or is about to attack. |
There are many anecdotal stories about unusual activity by animals going back hundreds of years, so I for one cannot completely dismiss the idea out of hand. Animals sense the world differently than humans, and there could in fact be some sort of electromagnetic or vibrational effect that researchers have not yet detected.
A reasonable response on earthquakes and animal behaviour by the U.S. Geological Survey can be read here, and a good article by the National Geographic can be found here. Geologists around the world have been following a story coming out of Italy regarding the failure of seismologists for failing to predict or warn the local populace before a deadly earthquake in Italy that killed several hundred people in 2009. It's one thing to say geologists can't predict earthquakes, and quite another to say they didn't predict it enough in the aftermath. Seismologists walk a fine line.
Speaking of kitties and strange behaviour, if you see these eyes, run for your life. Aliens have taken over your cat's soul....
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Comic art by Zeo |
Question 6: In California, we are waiting for the BIG ONE! True or False??
When I talk to groups about this question, I make sure to say "the BIG ONE" in capital letters. How do you say something in capital letters? You do it in a deep baritone voice with your hand cupping the microphone; it's very dramatic.
So what is the answer? Well, actually the question is wrong and requires a bit of modification. Let's try it again, and in that deep baritone voice:
In California, we are waiting for the BIG ONES!
There, that's better. If we can't predict earthquakes, then how can this statement be possible? Doesn't it require the ability to predict earthquakes? Yes, it does. So the statement must be false. But it is not. The answer is TRUE!
Predicting earthquakes is not possible in the short term, as in hours or days, but a great deal can be said about the probability of earthquakes in a particular area over a period of decades. We can do this on the basis of the historical and prehistorical record of earthquakes along a particular fault zone, and by analysis of building stresses and tilting over a large region, as revealed by GPS stations and other related technology Check out the methodology of the 2007 Working Group on California Earthquake Probabilities in this USGS PDF file.
As can be found on the map above, numerous fault zones represent a threat to the state of California. The fault zones are of different lengths, and therefore some will produce smaller quakes, but several are capable of producing large shocks approaching magnitude 7, and maybe even larger. These include the San Jacinto fault, the Owens Valley fault, the Hayward and Calaveras faults, and others. Even more important is the fact that the San Andreas itself is not a single monolithic fault zone. It has segments that behave independently. This was shown in 1857 and 1906, when completely different sections of the fault gave way, producing shocks that approached magnitude 8.
The most recently published studies show that earthquakes of 6.7 magnitude or greater are a virtual certainty over the next 30 years. The chance for an even greater quake is ominous, exceeding 70% for a magnitude 7.0, and a lesser, but still significant chance of even larger events. In a way, one of these quakes has already occurred, even though it was just south of the state: the El Mayor-Cucapah quake this year in northern Baja California was a magnitude 7.2 event.
Another wild card is the possibility of a large quake along the Cascadia subduction zone in the northernmost part of the state. It was not included in the probabilities, but numerous magnitude 7 quakes have taken place in that region in recent decades.